1. Technical Field
The present invention relates to a contactless (non-contact) ignition system for an internal combustion engine for automatically subjecting ignition timing to spark advance control and spark retardation control from a low rotational speed range to a high rotational speed range.
2. Related Art
As a contactless ignition system for an internal combustion engine of the related art, for example, at the time of rotation of a rotor having magnetic poles, a generating coil charges an induced voltage into an ignition charge and discharge condenser, and electrical charge charged into the ignition charge and discharge condenser is supplied to an ignition coil through switching elements that are switched by a voltage induced by a trigger coil.
In this type of contactless ignition system, if the rotational speed of the internal combustion engine, namely the rotational speed of the rotor, is increased, then together with that increase in speed the charge discharge timing of the ignition charge discharge condenser is advanced, and finally the rotational speed of the internal combustion engine is increased in excess of a set rotational speed and sometimes results in damage to the engine.
Devices adopting a governor mechanism and devices utilizing electronic control have therefore been proposed as devices for preventing overspeed of an internal combustion engine.
However, the governor mechanism requires a large operating space because of expansion and contraction effects while rotating integrally with a crank shaft, and there is the drawback that lifespan is shortened due to mechanical operation.
Also, with an engine overspeed prevention device that uses electronic control, there is a problem that because complicated electronic circuitry is used it is not possible to realize cost reduction.
The present invention has been conceived in view of the above described situation, and an object of the invention is to provide a compact and inexpensive contactless ignition system for an internal combustion engine that can improve starting performance and horsepower while causing advancement of ignition timing from low engine speed to normal engine speed, and that can prevent engine overspeed by causing retardation of ignition timing at above normal engine speed.
In order to achieve this object, a contactless ignition system for an internal combustion engine of the present invention comprises a rotor having magnetic poles arranged either side of a magnet, a core with two legs, arranged opposite the rotor, wound with a trigger coil on the one leg and with a generating coil on the other leg positioned opposite to the rotational direction of the rotor with respect to the one leg, an ignition charge discharge condenser for charging an induced voltage of the generating coil, a first switching element, triggered to be conductive when an induced voltage of the generating coil has reached a predetermined (specified) trigger level, for supplying a voltage charged in the ignition charge discharge condenser to an ignition coil, a trigger control condenser for charging induced voltages of the generating coil and the trigger coil, and a second switching element for inhibiting a trigger of the first switching element caused by induced voltage of the generating coil for a specified time following charge of the trigger control condenser.
In the present invention, at the time of startup, since ignition timing of the internal combustion engine is advanced, kick back (a phenomenon where a piston is pushed back immediately after ignition and the crankshaft rotates backwards due to piston speed being slow when starting) does not occur, and stable startup and increased speed can be expected. Also, in a normal engine speed range, it is possible to sufficiently maintain horsepower of the engine by sufficiently advancing the ignition timing. On the other hand, in a high engine speed region in excess of the normal engine speed, since the ignition timing can be retarded there is the advantage that it is possible to prevent engine overspeed.
As a preferred embodiment, it is possible for the second switching element to be a transistor that short-circuits the two ends of the trigger coil within a specified time of discharge of the trigger control condenser, to inhibit triggering of the first switching element. In this way, triggering of the first switching element can be implemented using a low cost circuit structure.
As another preferred embodiment, it is possible for the trigger control condenser to comprise a time constant circuit for determining a discharge time constant of the trigger control condenser in order to achieve ignition timing retardation control. In this way, there is the advantage that it is possible to select rotational speed of the engine that causes the ignition timing retardation to start easily and with high precision by setting the discharge time constant of the time constant circuit.
As another preferred embodiment, it is possible to provide a circuit protection trigger circuit to trigger the first switching element in a high voltage below capacity voltage of the ignition charge discharge condenser. In this embodiment, charge volume does not go beyond capacity voltage of the ignition charge discharge condenser. Therefore, it is possible to prevent damages of each section of the circuit including the ignition charge discharge condenser.